Coin and Paper Money Collecting/Silver tarnish
If I see a silver coin for sale that is 100 or more years old and has no tarnish or toning , should I assume it has been cleaned ?
The age of a coin does not determine its specific patina or life history. There are millions of coins well over 100 years old that have nice original bright untarnished patinas or surfaces.
When a coin is struck the surface can actually liquify under the intense pressure of the stamping process. These pressures were higher once steam driven presses were introduced in 1836. Before that many of the presses were operated manually. This process leaves the coin with a hard smooth surface that is resistant to oxygen molecules. Once this surface is compromised by handling or improper storage oxygen molecules can attach themselves to the micro cracks and scratches creating a layer of silver oxide - also know as Tarnish.
This tarnish can be removed but often the removal adds additional scratches and crevasses that will draw more oxygen molecules in faster resulting in more tarnish at a faster rate. This is why your silver flatware can sit unused and untarnished for decades. If you improperly polish it using abrasives the tarnish will show up in a few days or weeks making polishing a regular routine going forward.
So if a coin has been properly cared for and it was minted after 1836 you should not suspect cleaning until you have had a chance to inspect it in person. In the next few weeks we will be adding articles on how to determine if a coin has been cleaned to our website - www.necoinexchange.com.
Thanks for your question.
New England Coin Exchange